Spluttering after 5000 revs wont pik up fitted with k and n and sport cans also once warm revs are high

If this has happened since fitting the K&N is most likely a jetting problem, try using the choke at 5000rpm if that helps go up a size in the main jets, if it gets worse go down a size. I cant remember if the 88 still had CV carbs, but air turbulance can cause the CV carbs to open erraticly as they are designed to **** from the air box which supplies air evenly to all carbs